416 



THE SKIN. 



Sebaceous Glands. The sebaceous glands are racemose 

 glands, and discharge their product sebum into the hair-folli- 

 cles of large hairs, as upon the scalp, while in other portions of 

 the body, as the forehead, where the hairs are small, the hair pro- 

 jects from the mouth of the sebaceous gland, and is more like an 

 appendage than a separate structure. 



C. 



^ 



FIG. 233. (7, Epidermis; D, corium; P, papillae; 8, sweat-gland duct; r, arterial 

 and venous capillaries (superficial or papillary plexus) of the papillae (deep plexus 

 is partly shown at lower margin of the diagram) ; rs, an intermediate plexus, an 

 outgrowth from the deep plexus, supplying sweat-glands and giving a loop to hair- 

 papilla (after Eanvier). 



Composition of Sebum. The sebum, or sebaceous matter, is of 

 an oily nature. It contains albumin, fat, and cholesterin. The 

 vernix caseosa which covers the infant during the latter part of 

 fetal life is of the same character, consisting principally of fat 

 with epithelium. At the temperature of the body the sebum is 

 fluid, but it solidifies on the surface of the skin. Its office is 



